As a method for reducing iron oxide contained in an iron-oxide containing material such as an iron ore to thereby produce reduced iron, attention has been paid to a reduced iron production process in which a comparatively easily available charcoal material such as coal is used as a carbonaceous reducing material for reducing iron oxide. In the reduced iron production process, an agglomerate including an iron-oxide containing material and a carbonaceous reducing material is supplied onto a hearth of a rotary hearth furnace, and the agglomerate is heated due to gas heat transfer and radiant heat by a heating burner provided in a heating section inside the rotary hearth, so as to reduce iron oxide and produce reduced iron. After that, heated substances are cooled when they are passing through a non-heating section inside the rotary hearth furnace, and are then discharged to the outside of the furnace. The heated substances discharged to the outside of the furnace are, for example, classified into magnetically attracted substances and non-magnetically attracted substances by a magnetic separator. The magnetically attracted substances are recovered as an iron source.
In the aforementioned reduced iron production process, exhaust gas is generated by combustion in the heating burner. When the concentration of oxidizing gas such as carbon dioxide, moisture, etc., in the exhaust gas is increased, the reducing rate of iron oxide cannot be increased satisfactorily. Therefore, in the rotary hearth furnace exhaust ports etc., are provided at suitable places so that the exhaust gas inside the furnace can be discharged to the outside of the furnace. However, a means for supplying an agglomerate onto the hearth of the rotary hearth furnace, a means for discharging heated substances which have been heated in the rotary hearth furnace to the outside of the furnace, etc. communicate with the outside of the furnace directly. Therefore, when the exhaust gas inside the furnace is sucked and discharged to the outside of the furnace, outside air may flow into the furnace from the outside of the furnace accordingly. The outside air flowing in contains oxidizing gas such as oxygen, causing reduction in the reducing rate of reduced iron.
Patent Literature 1 has proposed a method for producing reduced iron, in which a flow of in-furnace gas is controlled properly to prevent oxidizing gas from inhibiting reduction. The method for producing reduced iron performs sequentially in a moving direction of a hearth: a starting material supplying step of charging a starting material including a carbonaceous reducing material and an iron-oxide containing material into a rotary hearth furnace, a step of heating/reducing step of heating the starting material and reducing iron oxide in the starting material to thereby produce reduced iron, a melting step of melting the reduced iron, a cooling step of cooling the melted reduced iron, and a discharging step of discharging the cooled reduced iron to the outside of the furnace. In the method for producing reduced iron, a flow rate adjusting partition wall for controlling a flow of in-furnace gas is provided in the furnace so that the flow of the in-furnace gas in the cooling step can be formed in a moving direction of a hearth. In addition, the aforementioned literature also suggests that the flow rate adjusting partition wall for controlling the flow of the in-furnace gas is provided in the furnace so that the pressure of the in-furnace gas in the melting step can be made higher than the pressure of the in-furnace gas in any other step.